This invention relates to a recording and reproducing device suitable for application to a variable-velocity playback type digital video recording and reproducing device capable of performing smooth and good-response variable-velocity reproduction, and a method of reproducing video information on a variable-velocity basis.
A digital video recording and reproducing device using a hard disk is normally large in memory capacity and needs a long access time. An information reading system using buffer memories provided in two-bank configurations has been adopted to reduce this access time. In the present system, video information is read from the other of one pair of general-purpose buffer memories when video information is written into one of the pair. Thus, the switching between the writing of the video information into one buffer memory and the reading of the video information from the other buffer memory is periodically done to sequentially record and reproduce or play back the video information. A dual port memory is known as a memory device for implementing such functions on a unitary basis.
FIG. 8 is a conceptional view showing a configuration of this type of digital video recording and reproducing device. In FIG. 8, a write and read-only controller 2 is electrically connected to a hard disk 1 so as to perform such control as to read video information corresponding to continuous m frames from video information corresponding to n frames. A keyboard 5 is electrically connected to the controller 2 to provide instructions for a playback velocity for video information through the use of a search dial SA provided in the keyboard 5.
Buffer memories 3A and 3B provided in two-bank configurations are electrically connected to the controller 2. Video information is read from the hard disk 1 in accordance with a reproduce or playback velocity and alternately written into the buffer memories 13A and 13B. In order to locate the start of an image or picture, for example upon video editing work executed by using this type of digital video recording and reproducing device, the image must be normally played back slowly. At this time, the image is reproduced at an arbitrary playback velocity (corresponding to a velocity given by an operator) less than or equal to a one-time velocity.
This playback velocity is specified or designated by the search dial 5A. A playback circuit 4 is electrically connected to the output-stage sides of the buffer memories 3A and 3B so that video information alternately read from the buffer memories 3A and 3B is reproduced. In this type of recording and reproducing device, the video information is read from each of the buffer memories 3A and 3B based on a bank period or cycle T to simplify an algorithm wherever practicable. The bank cycle T indicates a period in which the video information is written into or read from each of the buffer memories 3A and 3B.
Operation in a one-time velocity playback mode will next be described. First, an operator designates a playback velocity. Video information is read into the buffer memory 3A from the hard disk 1 in frame units at the designated playback velocity. At this time, video information corresponding to m frames are collectively read from the hard disk land written into the buffer memory 3A.
When the writing of the video information into the buffer memory 3A is completed, the bank cycle T is switched to another as shown in FIG. 9. The bank cycle T is always constant regardless of the playback velocity designated by the operator and is changed every m frames. With its changeover, the writing of video information into the buffer memory 3B is started and at the same time the reading of video information from the buffer memory 3A to the playback circuit is started. The video information read from the buffer memory 3A is reproduced by the playback circuit 4.
Further, when the writing of the video information into the buffer memory 3B and the reading of the video information from the buffer memory 3A are completed, the bank cycle T is switched to another. With its switching, the reading of video information from the buffer memory 3B is started and at the same time the writing of video information into the buffer memory 3A is started. The video information read from the buffer memory 3B is reproduced by the playback circuit 4.
Thus, the video recording and reproducing device using the buffer memories 3A and 3B provided in the two-bank configurations has a feature in that if a one-time velocity playback mode is adopted, video information can be sequentially recorded and reproduced without depending on an expensive dual port memory.
On the other hand, when an arbitrary playback velocity (including a still playback zero velocity) less than or equal to a one-time velocity is designated, a frame skip or jump will occur upon bank switching.
When the operator locates the start of a picture or image through the use of the search dial 5A, for example, a playback velocity less than or equal to a one-time velocity is designated. Video information is read into each of the buffer memories 3A and 3B from the hard disk 1 in frame units in accordance with this playback velocity. However, the playback velocity designated by the operator varies every moment for video retrieval. Further, a long access time is required to read the video information from the hard disk 1 to the buffer memories 3A and 3B in the frame units.
Therefore, a considerable time is required until the video information is outputted to the playback circuit 4 since the operator has designated the playback velocity. Thus, a problem arises in that variable-velocity reproduction very poor in response would be made.
In the conventional recording and reproducing device as well, the switching between the buffer memories 3A and 3B is performed every m frames on the basis of the bank cycle T regardless of the playback velocity.
Even when, for example, a video start portion approaches and at this time, it is desired to further sequentially read the video information of one buffer memory 3A without depending on the previously-designated playback velocity in order to slowly play back the video information thereof, the buffer memory 3A is switched over to the buffer memory 3B.
Therefore, the video information stored in the other buffer memory 3B must be read into the playback circuit 4 for slow reproduction in spite of the fact that it is desired to read the video information corresponding to the same frames into the playback circuit 4 from the buffer memory 3A. Thus, video information corresponding to continuous frames are not read from the buffer memories 3A and 3B and video information corresponding to discontinuous or skipping frames are outputted to the playback circuit 4. This offers a problem that a so-called frame skip or jump occurs and hence smooth slow reproduction cannot be achieved.
Thus, when reading control is performed while an algorithm for determining frames for video information to be written into the buffer memories 3A and 3B from the hard disk 1 and an algorithm for determining frames for video information to be outputted to the playback circuit 4 from the buffer memories 3A and 3B are being associated with one another, the frame units to be handled differ from each other between the writing of the video information to the buffer memories 3A and 3B and the reading of the video information from the buffer memories 3A and 3B, whereby the conventional variable-velocity playback system will result in a very complex one.
With the foregoing problems in view, it is therefore an object of the present invention to provide a recording and reproducing device capable of eliminating the occurrence of frame jumps upon bank switching even if an externally-instructed playback velocity varies every moment, and a method of reproducing video information on a variable-velocity basis.
A recording and reproducing device of the present invention comprises recording means for storing video information corresponding to n frames (where n=0, 1, 2, 3 . . . ) therein, two memories for inputting video information corresponding to continuous m frames (where m less than n) from the recording means and outputting the video information while performing switching between a function for writing the video information therein and a function for reading the video information therefrom, reproducing means for playing back the video information outputted from the memories, instructing means for designating a velocity for playing back the video information by the reproducing means, and control means for performing control for alternately writing the video information corresponding to the m frames made continuous so that video information corresponding to several frames overlap, into the two memories based on the playback velocity specified by the instructing means, and performing control for determining a slow reproducible playback velocity range according to the video information corresponding to the m frames, correcting the playback velocity given by the instructing means so as to fall within the playback velocity range, and thereafter reading the video information corresponding to the corresponding frame determined based on the corrected playback velocity.
In the recording and reproducing device of the present invention, when a playback velocity is designated by the instructing means, video information corresponding to continuous m frames, including overlapped video information is alternately written into two memories based on the playback velocity. Along with this, a slow reproducible playback velocity range is determined from the video information corresponding to the m frames, including the video information corresponding to the overlap by the control means. The playback velocity given by the instructing means is corrected so as to fall within the playback velocity range. Further, a frame for video information is determined based on the corrected playback velocity and the video information corresponding to the frame is read into reproducing means from the two memories.
Thus, since the playback velocity is limited to the slow reproducible playback velocity range even if an operator designates such a large playback velocity as to develop a frame skip or jump, no frame jump occurs and the video information can be slowly reproduced based on the corrected playback velocity.
Consequently, a recording and reproducing device can be provided which is capable of reproducing a smooth image upon location of the start of the image, for example even if an externally-instructed playback velocity varies every moment, and quickly responding to playback instructions issued by the operator.
In a method of reproducing video information on a variable-velocity basis, an algorithm related to control on the reading of video information into a hard disk and an algorithm related to control on the reading of video information from each buffer memory can be separated from one another. Thus, a recording and reproducing device can be constructed which makes it possible to simplify its system and is strong against disturbance.
The above-described recording and reproducing device is extremely suitable for application to a variable-velocity playback type digital video recording and reproducing device.